Acetic acid production by carbonylation includes continuously reacting methanol and carbon monoxide in the presence of a catalyst in a reactor. The reaction mixture present in the reactor comprises a transition metal, which may be a Group 9 metal, which may be iridium and/or rhodium, and may further include one or more solvents, water, various stabilizers, co-catalysts, promoters, and the like. Reaction mixtures known in the art may comprise acetic acid, methyl acetate, methyl iodide, hydrogen iodide, a hydrogen iodide promoter, and the like.
A complex network of interdependent equilibria involving liquid acetic acid reaction components exists in the reactor, which include those directed to the formation of acetic acid, as well as those directed to the formation of various impurities which are also produced in the reactor. Impurities which may be present in acetic acid include permanganate reducing compounds (PRCs) such as acetaldehyde. Accordingly, acetic acid processes disclosed in the art may further include various purification processes and control schemes wherein impurity formation is minimized and/or impurities produced are removed from the process or converted into product acetic acid.
Various impurities present in the produce acetic acid are difficult to remove. There is a need to control and monitor purification systems in various aspects of an acetic acid production process.